Fuel cell system including fuel processor and managing method thereof

ABSTRACT

A fuel cell system including a fuel processor, and a method of operating the fuel cell system, the fuel cell system includes: a reformer that reforms a hydrocarbon group fuel source into a reformed gas; a burner that heats the reformer; a CO remover unit that removes CO from a reformed gas generated by the reformer; a stack to generate electricity using the reformed gas; a first burner fuel supply line to supply the hydrocarbon group fuel source to the burner; and a second burner fuel supply line to supply the reformed gas from the CO remover unit to the burner.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No.2007-105788, filed on Oct. 19, 2007, in the Korean Intellectual PropertyOffice, the disclosure of which is incorporated herein in its entiretyby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Aspects of the present invention relate to a fuel cell system thatincludes a fuel processor, and a method of operating the fuel cellsystem.

2. Description of the Related Art

A fuel processor generally has a configuration in which, after reforminga hydrocarbon group fuel source, into a reformed gas suitable for use onelectricity generation reaction in a fuel processor, the reformed gas issupplied to an anode of a stack of a fuel cell system, to drive theelectricity generation reaction.

When a fuel is reformed in a fuel processor, the fuel undergoes a seriesof processes, such as, a desulphurization process, in which sulfurcomponents in the fuel source are reduced, a reforming process, in whichthe fuel source is reformed to a hydrogen-rich gas, and a CO removingprocess, in which CO produced as a by-product in the reforming processis removed. The reformed hydrogen-rich gas (also referred to as areformed gas) is supplied to an anode of the stack. Then, an electricitygeneration reaction occurs in the stack, between the reformed gassupplied to the anode, and air (oxygen) supplied to a cathode.

In order to efficiently operate a fuel cell system, it is necessary torapidly increase an initial start-up temperature. In particular, in thereforming process and the CO removing process, if the temperature is notabove a suitable level, a desired reaction result is not obtained. Thus,in order to rapidly operate the fuel cell system in a normal operationmode, it is necessary to be able to rapidly produce a reformed gas,through a rapid temperature increase at the initial start-up. Thereformed gas output from the fuel processor, before a normal operationis reached, cannot be supplied to the stack, or discharged to theoutside, and thus, a method of treating the reformed gas must beprovided.

Therefore, a fuel cell system must be manufactured to have a structurethat can be efficiently operated, in consideration of the above matters.

SUMMARY OF THE INVENTION

Aspects of the present invention provide a fuel cell system, in which afuel processor and a stack can be rapidly and efficiently operated, anda method of operating the fuel cell system.

According to an aspect of the present invention, there is provided afuel cell system comprising: a reformer that performs a reformingreaction of a fuel source; a burner that heats the reformer; a COremover unit that removes CO from a reformed gas generated by thereformer; a stack in which an electricity generation reaction, using thereformed gas, is performed; a first burner fuel supply line to supplythe fuel source to the burner; and a second burner fuel supply line tosupply the reformed gas from the CO remover unit, to the burner.

According to aspects of the present invention, the fuel cell system mayfurther comprise a third burner fuel supply line to supply an anode offgas, which is a surplus reformed gas from the stack, to the burner. Thesecond burner fuel supply line and the third burner fuel supply line maybe connected to each other, so that the second burner fuel supply line,or the third burner fuel supply line, can be selected by a first valve,to thereby supply a fuel to the burner.

According to aspects of the present invention, the fuel cell system mayfurther comprise first and second heat exchangers to preheat water thatis conveyed to the reformer, by absorbing heat from an exhaust gas fromthe burner, and the heat from the reformed gas from the reformer.

According to aspects of the present invention, the fuel cell system mayfurther comprise a warm water conveying line that conveys the waterheated by the reformer, to a warm water storage, through the second heatexchanger. The fuel cell system may further comprise a second valve thatcontrols the transport of warm water to the warm water storage, from thereformer, through the warm water conveying line, and controls thetransport of the reformed gas to the CO remover unit, from the reformer.

According to aspects of the present invention, the CO remover unit maycomprise a CO shifter and a CO remover, and the second burner fuelsupply line may be branched between an outlet of the CO shifter and anoutlet of the CO remover.

According to another aspect of the present invention, there is provideda method of operating a fuel cell system, comprising: heating a reformerusing a burner; supplying water to the reformer, when the temperature ofthe reformer reaches a first set temperature; performing a reformerreaction, by supplying a fuel source to the reformer, when thetemperature of the CO remover unit reaches a second set temperature;supplying a reformed gas that has passed through the CO remover unit, tothe burner, as a fuel for operating the burner, until the CO content inthe reformed gas is reduced to set content, or less; and supplying thereformed gas that has passed through the CO remover unit, to a stack,when the CO content in the reformed gas is sufficiently reduced.

According to aspects of the present invention, the method may furthercomprise supplying an anode off gas, which is surplus gas coming out ofthe stack, to the burner. The method may further comprise conveyingwater heated in the reformer, to a warm water storage, until thetemperature of the CO remover unit reaches a second set temperature.

According to aspects of the present invention, the first set temperaturemay be 500° C., the second set temperature may be 80° C., and the set COcontent may be 1 vol %.

Additional aspects and/or advantages of the invention will be set forthin part in the description which follows and, in part, will be obviousfrom the description, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the invention will becomeapparent and more readily appreciated, from the following description ofthe exemplary embodiments, taken in conjunction with the accompanyingdrawings, of which:

FIG. 1 is a block diagram of a fuel cell system, according to anexemplary embodiment of the present invention;

FIGS. 2A through 2C are block diagrams of operation modes of the fuelcell system of FIG. 1, according to exemplary embodiments of the presentinvention; and

FIG. 3 is a flow chart showing a start-up operation of the fuel cellsystem of FIG. 1, according to an exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the present embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to the like elementsthroughout. The embodiments are described below in order to explain thepresent invention by referring to the figures.

FIG. 1 is a block diagram of a fuel cell system, according to anexemplary embodiment of the present invention. Referring to FIG. 1, thefuel cell system includes: a stack 200 that performs an electricitygeneration reaction; and a fuel processor 100 that reforms hydrocarbongroup fuel source into a reformed fuel.

The fuel processor 100 includes a desulfurizer 110, a reformer 120, aburner 130, first and second heat exchangers 161 and 162, and a COremover unit 170. The CO remover unit 170 comprises a CO shifter 171 anda CO remover 172. The process of reforming the hydrocarbon group fuelsource is performed in the reformer 120. That is, hydrogen is producedin the reformer 120, which is heated by the burner 130, through areaction between the hydrocarbon group fuel source supplied from a fueltank 140, and steam supplied from a water thank 150, through a watersupply line 151. At this point, CO₂ and CO are produced as by-products.

If a fuel gas having a CO content of 10 ppm, or more, is supplied to thestack 200, electrodes therein are poisoned, and thus, the performance offuel cells of the stack 200 can be rapidly reduced. Thus, the CO contentin the fuel gas is reduced below 10 ppm, by disposing the CO shifter 171and the CO remover 172 at an outlet of the reformer 120. In the COshifter 171, a reaction of CO and steam, to produce CO₂, mainly occurs.In the CO remover 172, a reaction occurs to oxidize CO with oxygen. TheCO content in the reformed gas that has passed through the CO removerunit 170, is thereby reduced below about 10 ppm.

The desulfurizer 110 is disposed at an inlet side of the reformer 120,and removes sulphur components from in the hydrocarbon group fuelsource. If the reformed gas has a sulphur component of 10 ppb, or more,there is a high risk of poisoning the electrodes. Thus, the sulphurcomponents in the hydrocarbon group fuel source are removed, by thedesulfurizer 110. The first and second heat exchangers 161 and 162 heatwater from the water tank 150, which then enters the reformer 120,through the water supply line 151. The heat exchanger 161 absorbs heatfrom an exhaust gas from the burner 130, and the heat exchanger 162absorbs heat from the reformed gas exhausted from the reformer 120.

When the fuel cell system, having the fuel processor 100 and the stack200, is operated in a normal operation mode, the reformed gas isproduced by the fuel processor 100, and is supplied to the stack 200. Anelectricity generation reaction occurs in the stack 200, by reacting thereformed gas with an oxidant.

The burner 130 uses the hydrocarbon group fuel source, which is suppliedfrom the fuel tank 140, through a first burner fuel supply line 301. Thereformed gas that has passed through the CO remover unit 170 can also beused to operate the burner 130. The reformed gas can be supplied througha second burner fuel supply line 302 to the burner 130, from the COremover unit 170. An anode off-gas, which is surplus reformed gas thatis discharged from the anode 201 of the stack 200, can be also used asto operate the burner 130. The off-gas can be supplied to the burner130, through a third burner fuel supply line 303. That is, the burner130 can be operated using the fuels supplied through the three fuelsupply lines 301, 302, and 303.

The burner 130 not only uses the hydrocarbon group fuel source suppliedfrom the fuel tank 140, but also uses the reformed gas produced from thereformer 120. Methods of supplying the fuels to the burner 130, throughthe three fuel supply lines, will be described later. A first valve 181controls the supply of a particular fuel to the burner 130, byselectively opening the second burner fuel supply line 303 or the thirdburner fuel supply line 303.

The fuel cell system includes a warm water conveying line 304 to supplywater heated by the reformer 120, to a warm water storage 240. The waterheated by the burner 130 at a start-up operation (before performing anormal operation) is sent to the warm water storage 240, to be put toother uses. A second valve 182 is provided on an outlet side of thesecond heat exchanger 162, and controls whether the warm water istransferred from the reformer 120 to the warm water storage 240, throughthe warm water conveying line 304, or to the CO remover unit 170.

The stack 200 includes stacked unit cells. Each unit cell includes ananode 201, to which the reformed gas is supplied, and a cathode 202, towhich air (an oxygen source) is supplied. The stack 200 includes coolingplates 203 installed between several unit cells. Cooling water iscirculated through the cooling plates 203, to absorb heat generatedduring the electricity generation reaction. In FIG. 1, for convenienceof explaining, one anode 201 and one cathode 202 are depicted. However,in practice, a plurality of unit cells are employed, each including ananode 201, a cathode 202, and an electrolyte membrane (not shown)interposed therebetween. The cooling plates 203 are installed betweenevery five to six unit cells.

The fuel cell system includes: a cooling water storage 210, to storecooling water received from a water tank 220; a third heat exchanger 231to exchange heat absorbed by the cooling water from the stack 200, withthe water of the water tank 220; and a fourth heat exchanger 232 thatcools steam and air coming out from the cathode 202, using the water ofthe water tank 220. The cooled steam is sent to the water tank 150 ofthe fuel processor 100. The cooling water is circulated in the coolingplates 203 to cool the stack 200.

The fuel cell system having the above structure can be operated by asequence shown in FIG. 3. In order to start-up the fuel cell system, thehydrocarbon group fuel source is supplied to the burner 130, from thefuel tank 140, through the first burner fuel supply line 301, to heatthe reformer 120 (S1). When the temperature of the reformer 120 reachesa set temperature, for example, 500° C. (S2), water stored in the watertank 150 is supplied to the reformer 120, through the water supply line151 (S3). At this time, the reformed fuel is not produced, since thehydrocarbon group fuel source is not supplied to the reformer 120. Thus,only water is heated in the reformer 120, which is heated by the burner130. The heated water is transported from the reformer 120, to the warmwater storage 240, through the warm water conveying line 304, under thecontrol of the second valve 182 (refer to FIG. 2A).

The CO shifter 171 contacts the reformer 120, thus, the temperature ofthe CO shifter 171 is increased, when the reformer 120 is heated by theburner 130. The CO shifter 171 is heated to a set temperature, forexample, 80° C., or above, in order that a CO removal reaction can beappropriately performed. Thus, when the temperature of the CO shifter171 reaches at least 80° C. (S4), the hydrocarbon group fuel source inthe fuel tank 140 is supplied to the reformer 120, through thedesulfurizer 110 (S5). Thus, a reformer reaction is conducted, by whicha reformed gas having hydrogen as a main component is produced, byreacting the hydrocarbon group fuel source and the water.

At this point, the second valve 182 closes the warm water conveying line304, and opens a path to the CO shifter 171, to allow the reformed gasto be transferred from the reformer 120 to the CO shifter 171. However,at an early stage of operation, the CO remover unit 170 cannotsufficiently remove CO from the reformed gas. In order to preventelectrodes in the stack 200 from being poisoned by the CO, the contentof CO in the reformed gas, must be below about 10 ppm. For this purpose,the CO content at an outlet of the CO shifter 171 must be at least 1 vol%, or less. Until the CO content at the outlet of the CO shifter 171 isreduced to 1 vol %, or less, the reformed gas is not supplied to thestack 200. However, the reformed gas is supplied to the burner 130,through the second burner fuel supply line 302, from the CO shifter 171(S5) (refer to FIG. 2B). The valve 183 is installed at the outlet of theCO shifter 171, to return the reformed gas to the burner 130. However,the valve 183 can also be installed at the outlet of the CO remover 172,to return the reformed gas to the burner 130.

When the CO content at the outlet of the CO shifter 171 is reduced to 1vol %, or less, (S6), the fuel cell system is switched to a normaloperation mode and the reformed gas is supplied to the stack 200 (S7)(refer to FIG. 2C).

According to the configuration as described above, a fuel cell systemthat can be rapidly and smoothly operated and a method of operating thefuel cell system can be realized.

Although a few exemplary embodiments of the present invention have beenshown and described, it would be appreciated by those skilled in the artthat changes may be made in these embodiments, without departing fromthe principles and spirit of the invention, the scope of which isdefined in the claims and their equivalents.

1. A fuel cell system comprising: a reformer that produces a reformedgas from a source fuel; a burner that heats the reformer; a CO removerunit that removes CO from the reformed gas; a stack that generateselectricity using the reformed gas; a first burner fuel supply line toconvey the source fuel to the burner; and a second burner fuel supplyline to convey the reformed gas from the CO remover unit, to the burner.2. The fuel cell system of claim 1, further comprising a third burnerfuel supply line to convey an off-gas from the stack to the burner. 3.The fuel cell system of claim 2, further comprising a valve disposed atan intersection between the second burner fuel supply line and the thirdburner fuel supply line, to selectively control the conveyance of theoff-gas and the reformed gas, to the burner.
 4. The fuel cell system ofclaim 1, further comprising: a first heat exchanger to heat water usingan exhaust gas from the burner; and a second heat exchanger to receivethe water from the first heat exchanger, and to heat the water using thereformed gas that is exhausted from the reformer.
 5. The fuel cellsystem of claim 4, further comprising a warm water conveying line thatconveys the water from the second heat exchanger to a warm waterstorage.
 6. The fuel cell system of claim 5, further comprising a valvethat controls whether the water from the second heat exchanger isconveyed to the warm water storage, via the warm water conveying line,or the water is conveyed to the CO remover unit.
 7. The fuel cell systemof claim 1, wherein: the CO remover unit comprises a CO shifter, and aCO remover connected to the CO shifter, and the second burner fuelsupply line comprises a first branch connected to the CO shifter, andsecond branch connected to the CO remover.
 8. A method of operating afuel cell system comprising: heating a reformer using a burner; heatingwater in the reformer, once the reformer is heated to a firsttemperature; supplying a fuel source to the reformer to produce areformed gas, once a CO remover unit connected to the reformer reaches asecond temperature; supplying the reformed gas that has passed from thereformer through the CO remover unit, to the burner, when the CO contentof the reformed gas is greater than a set amount; and supplying thereformed gas from the CO remover unit to a stack, when the CO content inthe reformed gas is reduced to the set amount, or less.
 9. The method ofclaim 8, further comprising supplying an off-gas from the stack to theburner, after the reformed gas is supplied to the stack.
 10. The methodof claim 8, further comprising conveying the water heated by thereformer to a warm water storage, until the temperature of the COremover unit reaches the second temperature.
 11. The method of claim 8,wherein the first temperature is about 500° C., the second temperatureis about 80° C., and the set amount of the CO content is about 1 vol %.